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Podzols, also known as podosols, spodosols, or espodossolos, are the typical of or Taiga and also the typical soils of eucalypt forests and in southern Australia. In Western Europe, podzols develop on heathland, which is often a construct of human interference through grazing and burning. In some British with podzolic soils, are preserved under Bronze Age barrows.
The E horizon (or Ae in Canadian soil classification system), which is usually thick, is low in Fe and Al oxides and humus. It is formed under moist, cool and acidic conditions, especially where the parent material, such as granite or sandstone, is rich in quartz. It is found under a layer of organic material in the process of decomposition, which is usually thick. In the middle, there is often a thin horizon of . The bleached soil horizon, which always has a higher value than the horizons above and below it, goes over into a red or red-brown horizon (so-called Podzolic B). The colour is strongest in the upper part, and change at a depth of progressively to the part of the soil that is mainly not affected by processes; that is the parent material. The are designated by the letters A (topsoil), E ( soil), B (subsoil) and C (parent material).
In some Podzols, the E horizon is absent—either masked by biological activity or obliterated by disturbance. Podzols with little or no E horizon development are often classified as brown Podzolic soils, also called or inceptisols.
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Podzols cover about worldwide and are usually found under woody vegetation. By extent Podzols are most common in temperate and Taiga of the Northern Hemisphere but they can also be found in other settings including both temperate rainforests and tropical areas.Spaargaren, Otto. Podzols. Encyclopedia of Soil Science, pp. 580–581.
In South America Podzols occur beneath Nothofagus betuloides forests in Tierra del Fuego.
In the topsoil of acidic soils, organic matter (mostly from plant litter, the humus layer and ) together with Al- and Fe-ions, form organo-mineral complexes. These soluble Chelation then relocate with percolating water from the A horizon (or E horizon) to the B horizon. As a result of this, the E horizon (or Ae horizon in the Canadian system of soil classification) is left bleached and ash-grey in colour, while the B horizon becomes enriched with relocated organo-mineral complexes. The colour of B horizon is consequently red, brown or black, depending on the dominance of metal ions or organic matter. Usually, the boundary between the B and eluvial Ae (or E) horizon is very distinct, and sometimes a hardpan (or Ortstein) can form, as the relocated Fe and Al and organic matter increase mineral particles, cementing them into this compacted layer.
There are several reasons why these organo-mineral complexes immobilize in the B horizon: If during the eluviation process more Al- or Fe-ions bind to the organic compounds, the complex can flocculate as the solubility of it decreases with increasing metal to carbon ratio. Apart from that, a higher pH (or higher Ca content) in the lower can result in the breakdown of metal-humus complexes. In the lower soil layers, the organic complexing agents can be degraded by functioning . Already established complexes in the B horizon can act as a filter, as they adsorb the traveling complexes from the upper soil horizons. A decreased water conductivity due to higher clay content can also result in the early flocculation of organo-mineral complexes.
The relocated substances can sometimes separate in the illuvial horizons. Then, organic substances are mostly enriched in the uppermost part of the illuvial horizon, whereas Fe- and Al-oxides are mostly found in the lower parts of the illuvial horizon.
Podzolization also promotes the relocation of some nutrients (Copper, Iron, Manganese, Molybdenum and Phosphorus) that sometimes brings them closer to plant .
The term Podzols is used in the World Reference Base for Soil Resources (WRB) and in many national soil classification systems (in some of them, spelled Podsols).
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